The use of knitted base fabrics of large widths to reinforce waistbands or to increase their rigidity using the warp (or tricot) technique with long, synthetic monofilament weft inserts has already been described (EP-A-0 161 823).
These knitted base fabrics are cut in small strips corresponding to the width required to reinforce the waistband.
This type of base fabric has a certain number of disadvantages.
A first disadvantage is that the monofilament wefts cannot be correctly attached to the warp knitted fabric structure made up of multifilament yarns due to the fact that the binding points are very small and that the adhesion between the smooth filament yarns (monofilament or multifilament) is hazardous and disappears as a result of the mechanical and chemical treatments undergone during washing and dry-cleaning. As a result, the monofilament yarns come out of the structure and pass through the cloth of the waistband.
Another disadvantage of this type of knitted base fabric which is worth mentioning is that, given the spacing of the monofilament yarns (separated by the knots in the stitch), the selvedges of the cut strips have an abrasive surface.
To avoid these disadvantages it is necessary to deposit on both selvedges of the strip a continuous wad of synthetic resin covering the abrasive end of the monofilament yarns.
As a reinforcement for the waistband, it is also possible to use a composite fabric consisting of a nonwoven fabric knitted inside a long weft stitch (U.S. Pat. No. 4,980,930).
The purpose of the nonwoven fabric is to even and smoothen the surface of one of the fabric's faces. This even surface makes it possible to eliminate the necessity for a protective or screen forming fabric in the waistband. This specific configuration simplifies the fitting of the waistband and reduces its cost.
However, the two base fabrics described above have little or no elasticity in the direction of the warp, as this can only be obtained with highly elastic yarns.
For this purpose, it has been suggested that composite waistbands be used which are elastic in the direction of the warp and manufactured in small widths (waistband width of approximately 1.54 to 2.3 cm) using the knitting-crochet technique (U.S. Pat. No. 4,551,994).
The base fabric described in this document essentially consists of:
a warp knit fabric substrate made up of synthetic multifilament yarns, with elastic yarns deposited substantially parallel to the wales (in the direction of the warp); PA1 a monofilament yarn deposited on part of the width of the waistband by means of a pattern bar equipped with guides between the rows of short "weft" stitches; this monofilament yarn ensures rigidity in the direction of the width; PA1 a second multifilament weft yarn deposited in a strip parallel to that comprising the monofilament wefts; PA1 a multifilament yarn layer deposited in the form of a very short weft whose purpose is to form a screen and possibly patterns. PA1 the high manufacturing cost of the knitting; PA1 the finishing treatments (stabilization with a coating finish) performed in small widths; PA1 the yarn numbering of the monofilament yarns required for the purpose of rigidity and deposited using the warp pattern bar technique, which is limited in terms of thickness due to the fact that the yarn is necessarily folded back upon each to-and-fro passage inside the reinforced strip. PA1 a using a warp knitting machine with weft inserts to produce a composite base fabric comprising: PA1 thermofixing the composite base fabric thus obtained so as to avoid its shrinkage upon subsequent thermal treatments; PA1 depositing a film forming coating comprising a cross-linkable resin on the face of the fabric substrate in contact with the elastic yarns and the weft yarns; PA1 drying and cross-linking the film forming coating to ensure the fixing of the weft yarns on the fabric substrate; PA1 submitting the composite base fabric to a relaxation treatment in order to slacken the elastic yarns and to eliminate the residual tensions which have possibly appeared in the course of the previous steps. PA1 a warp knit fabric; PA1 a fabric substrate inserted in the warp knit fabric; PA1 elastic yarns inserted substantially parallel to the wales according to a lap on one needle configuration; PA1 long weft yarns inserted in the warp knit fabric without participating in the formation of its stitches; PA1 a film forming coating on the face of the fabric substrate in contact with the elastic yarns and the weft yarns.
The main purpose of this multilayer base fabric is to simplify the fitting of the waistband. However, it has major disadvantages such as: